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PIC 'burnt'

 
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Einly
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PIC 'burnt'
PostPosted: Sat Dec 14, 2002 4:42 am     Reply with quote

Dear all,

I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.

However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.

Does anybody know how to solve this?

Thanks

Einly
___________________________
This message was ported from CCS's old forum
Original Post ID: 10045
R.J.Hamlett
Guest







Re: PIC 'burnt'
PostPosted: Sat Dec 14, 2002 6:17 am     Reply with quote

:=Dear all,
:=
:=I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.
:=
:=However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.
:=
:=Does anybody know how to solve this?
:=
:=Thanks
:=
:=Einly
How are you 'clamping' the motor outputs?. You need to have reverse diodes across the output transistors, or when you remove the power, there is a risk of the inductive overshoot, driving the output of the transistor massively -ve (or +ve for the PNP drivers). If this happens, then current will flow from the collector to base of the transistors, and this could easily damage the PIC. Also have you got current limiting resistors in the drives (otherwise the PIC, could be having to source/sink more than the specified maximum (normally about 20mA) of current. Normally limiting resistors around 200ohm should be used (depending on the Vbe of the driver transistors), otherwise the PIC can end up damaged.
If the output currents are reasonably high, you may well have to consider darlington drivers (depends on the Hfe of the output transistors), or FETs, since otherwise the drive current required may be beyond the capability of the chip.
Are you being careful when switching from forward to reverse? (and vice versa). Remember that unless you switch 'off' the currently used drivers, before switching 'on' the second pair, you can end up with both drivers on at the same time, and a massive current 'spike'.
If you are really having problems, look at using opto-couplers between the PIC, and the drivers.
It should be perfectly possible to run the PIC off the same supply, but you may need to have a 'dirty', and a 'clean' rail, and add an extra inductor/capacitor filter between these.
I am using FET H-bridge drivers here, driven directly off a PIC for the +ve drive, and via a FET 'and' gate to a PWM source, to control currents of over 50A, without problems.

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 10046
oscar
Guest







Re: PIC 'burnt'
PostPosted: Mon Dec 16, 2002 3:45 pm     Reply with quote

:=Dear all,
:=
:=I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.
:=
:=However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.
:=
:=Does anybody know how to solve this?
:=
:=Thanks
:=
:=Einly

Dear Einly,

First thing I would do is disconnect the PIC drive pins from the H-bridge then take the Vcc you use to power the PIC and connect it to one of the inputs of the H-bridge. Measure the current flow and if that current is greater than 25mA then you can't use the PIC to drive the H-bridge directly.

If it's over 25mA go get a Toshiba TDS62783(digikey has them) darlington source driver to buffer your PIC drive. If you don't want to use the TDS62783 you can use an N-FET with the appropriate Id (drain current rating) on each bridge input, use a pull-down on the source. Hope that helps.

o.
___________________________
This message was ported from CCS's old forum
Original Post ID: 10075
John Lamb
Guest







Re: PIC 'burnt'
PostPosted: Tue Dec 17, 2002 1:36 pm     Reply with quote

I have done a similar thing, a couple easy outs are to look at chucks design at
www.mcmanis.com/~cmcmanis/robotics/ h-bridge/h-bridge.html

I have used this with the 16f877 successfully.

The other option is to look at national.com, they offer quite a few H-bridge IC's, and you can often get them in samples for free. Check out
<a href="http://www.national.com/parametric/0,1850,1075,00.html" TARGET="_blank">http://www.national.com/parametric/0,1850,1075,00.html</a>

Good Luck


:=:=Dear all,
:=:=
:=:=I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.
:=:=
:=:=However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.
:=:=
:=:=Does anybody know how to solve this?
:=:=
:=:=Thanks
:=:=
:=:=Einly
:=How are you 'clamping' the motor outputs?. You need to have reverse diodes across the output transistors, or when you remove the power, there is a risk of the inductive overshoot, driving the output of the transistor massively -ve (or +ve for the PNP drivers). If this happens, then current will flow from the collector to base of the transistors, and this could easily damage the PIC. Also have you got current limiting resistors in the drives (otherwise the PIC, could be having to source/sink more than the specified maximum (normally about 20mA) of current. Normally limiting resistors around 200ohm should be used (depending on the Vbe of the driver transistors), otherwise the PIC can end up damaged.
:=If the output currents are reasonably high, you may well have to consider darlington drivers (depends on the Hfe of the output transistors), or FETs, since otherwise the drive current required may be beyond the capability of the chip.
:=Are you being careful when switching from forward to reverse? (and vice versa). Remember that unless you switch 'off' the currently used drivers, before switching 'on' the second pair, you can end up with both drivers on at the same time, and a massive current 'spike'.
:=If you are really having problems, look at using opto-couplers between the PIC, and the drivers.
:=It should be perfectly possible to run the PIC off the same supply, but you may need to have a 'dirty', and a 'clean' rail, and add an extra inductor/capacitor filter between these.
:=I am using FET H-bridge drivers here, driven directly off a PIC for the +ve drive, and via a FET 'and' gate to a PWM source, to control currents of over 50A, without problems.
:=
:=Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 10099
Einly
Guest







Re: PIC 'burnt'
PostPosted: Thu Dec 19, 2002 7:37 am     Reply with quote

Dear sir,

May I know how should the current limiting resistor placed?
Where should it connected to? Is it between the output pin from the pic chip and the base of the transistor? Or is it between the power supply and the Vdd pin of the pic? How is it determined by looking at the Vbe?

If I am using a FET bridge, do I need to connect the diodes and current limiting resistor?

Thanks.

Einly
,
:=:=
:=:=I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.
:=:=
:=:=However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.
:=:=
:=:=Does anybody know how to solve this?
:=:=
:=:=Thanks
:=:=
:=:=Einly
:=How are you 'clamping' the motor outputs?. You need to have reverse diodes across the output transistors, or when you remove the power, there is a risk of the inductive overshoot, driving the output of the transistor massively -ve (or +ve for the PNP drivers). If this happens, then current will flow from the collector to base of the transistors, and this could easily damage the PIC. Also have you got current limiting resistors in the drives (otherwise the PIC, could be having to source/sink more than the specified maximum (normally about 20mA) of current. Normally limiting resistors around 200ohm should be used (depending on the Vbe of the driver transistors), otherwise the PIC can end up damaged.
:=If the output currents are reasonably high, you may well have to consider darlington drivers (depends on the Hfe of the output transistors), or FETs, since otherwise the drive current required may be beyond the capability of the chip.
:=Are you being careful when switching from forward to reverse? (and vice versa). Remember that unless you switch 'off' the currently used drivers, before switching 'on' the second pair, you can end up with both drivers on at the same time, and a massive current 'spike'.
:=If you are really having problems, look at using opto-couplers between the PIC, and the drivers.
:=It should be perfectly possible to run the PIC off the same supply, but you may need to have a 'dirty', and a 'clean' rail, and add an extra inductor/capacitor filter between these.
:=I am using FET H-bridge drivers here, driven directly off a PIC for the +ve drive, and via a FET 'and' gate to a PWM source, to control currents of over 50A, without problems.
:=
:=Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 10137
R.J.Hamlett
Guest







Re: PIC 'burnt'
PostPosted: Fri Dec 20, 2002 3:17 am     Reply with quote

:=Dear sir,
:=
:=May I know how should the current limiting resistor placed?
:=Where should it connected to? Is it between the output pin from the pic chip and the base of the transistor? Or is it between the power supply and the Vdd pin of the pic? How is it determined by looking at the Vbe?
:=
Between the PIC, and the base of the transistor. The resistor is determined by the difference between the PIC's output voltage, and Vbe, together with the maximum current. Generally it is better for the PIC, for the resistor to be too large, and this doesn't matter, _provided_ the hfe of the transistor is sufficient for it still to switch the current concerned. For instance if you want to switch 1A, and have a transistor with an hfe of 200, then you only need to actually deliver 5mA into the base. However if you need to control 10A, and have a transistor with an hfe of 90, then you need to deliver 110mA into the base. Since power transistors typically have a lower hfe than small signal types, this is why the darlington configuration is often needed. You have to also remember that though each output can deliver 20mA, the total drawn on several of the pins is also limited, so it is easy to find this figure being the limit...

:=If I am using a FET bridge, do I need to connect the diodes and current limiting resistor?
:=
You still need some method of dealing with the current when the switches are off (it wants to go somewhere...). On a FET, you don't need a limiting resistor in this sense, but it is common to have a resistor, which slightly slows the switching edges, as part of the HF design.
Yes you do need diodes. If you look at the typical application notes for 'off the shelf' H-bridges, you will find they either have these diodes shown between the drive pins, and the supply rails, or have a high voltage 'forward' diode in series with one of the drivers, combined with a snubber resistor. You need to have somewhere for the energy in the 'loop' to discharge when the bridge is disconnected, or it is a failure waiting to happen... However a lot of power FET's, have such a diode 'built in', and provided the rating of this is adequate, this removes the need to provide a seperate part.

:=Thanks.
:=
:=Einly
Happy switching. :-)


:=:=:=
:=:=:=I'm using PIC16F876 to control direction of rotation of a DC motor through a h-bridge circuit. Pin B0,1,2,3 is connected to 4 separate high power transistors in the h-bridge.
:=:=:=
:=:=:=However, I have burned 3 PIC chips and I suspected that this is due to the high current supplied to the motor. Thus, I have used 2 separate power supplies for the pic and the h-bridge circuit which is used to drive the motor. It seems ok, but I hope that I can use a single power supply for the two circuits.
:=:=:=
:=:=:=Does anybody know how to solve this?
:=:=:=
:=:=:=Thanks
:=:=:=
:=:=:=Einly
:=:=How are you 'clamping' the motor outputs?. You need to have reverse diodes across the output transistors, or when you remove the power, there is a risk of the inductive overshoot, driving the output of the transistor massively -ve (or +ve for the PNP drivers). If this happens, then current will flow from the collector to base of the transistors, and this could easily damage the PIC. Also have you got current limiting resistors in the drives (otherwise the PIC, could be having to source/sink more than the specified maximum (normally about 20mA) of current. Normally limiting resistors around 200ohm should be used (depending on the Vbe of the driver transistors), otherwise the PIC can end up damaged.
:=:=If the output currents are reasonably high, you may well have to consider darlington drivers (depends on the Hfe of the output transistors), or FETs, since otherwise the drive current required may be beyond the capability of the chip.
:=:=Are you being careful when switching from forward to reverse? (and vice versa). Remember that unless you switch 'off' the currently used drivers, before switching 'on' the second pair, you can end up with both drivers on at the same time, and a massive current 'spike'.
:=:=If you are really having problems, look at using opto-couplers between the PIC, and the drivers.
:=:=It should be perfectly possible to run the PIC off the same supply, but you may need to have a 'dirty', and a 'clean' rail, and add an extra inductor/capacitor filter between these.
:=:=I am using FET H-bridge drivers here, driven directly off a PIC for the +ve drive, and via a FET 'and' gate to a PWM source, to control currents of over 50A, without problems.
:=:=
:=:=Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 10152
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