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Switching Regulator Noise

Power source supplies 12 volts @ up to 10 Amps surge for a motor. A boost switcher converts this voltage to a level needed to charge the 12V battery (the data sheet shows a circuit for that, LT3796). A steering circuit sele cts the DC input when above 10V or the battery when the input is below 10 v olts. A limiter/switch limits the voltage to the motor to 12V (manufacture r warning) and acts as a cutoff when over current.

The rest of the electronics needs 5 and 3.3 volt supplies with one 5V suppl y providing up to 300 mA mostly for the LCD back light LED current. The re st is maybe 50 mA combined. Some of this is sensitive analog circuitry. O ne device we are measuring has a nominal signal of 10 mV. The sensors are all slow, so power supply noise can and will be filtered in analog before t he ADC and in digital in the delta-sigma ADC.

The switching charger circuit and the motor controller will be on a separat e board at the back of the chassis, perhaps two feet/500 mm from the front of the chassis where the front panel, battery and controller board are. Th e motor is mostly in the back.

Some are concerned about the power wasted in the linear regulators for 5 an d 3.3 volts and want them to be switchers. Rather than making them switche rs, I'm thinking add a 7V switcher on the rear board to supply a voltage fo r linear regulators on the front controller board. Then the wasted heat th at the controller board has to dissipate is much lower.

I'd really like to see a display used that doesn't consume so much current, but that ain't go'na happen. The rest of the electronics is pretty low po wer even when using power from the 12V rail.

There is some irony in the fact that one engineer is opposed to driving the linears directly from 12V because the higher temps will lower the reliabil ity of the linear parts while some mechanical parts of the machine are desi gned for a lifetime of weeks. I'm pretty sure running a linear at 80 ?

Does adding a 7V switcher to the PSU board in the rear of the chassis sound like a reasonable approach to reducing the power dissipated in the linear regulators on the front board?

What would you do?

--

  Rick C. 

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Reply to
Rickster C
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Just throw a AOZ1282 at it already.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

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10 volts. A limiter/switch limits the voltage to the motor to 12V (manufacturer warning) and acts as a cutoff when over current.

The rest of the electronics needs 5 and 3.3 volt supplies with one 5V supply providing up to 300 mA mostly for the LCD back light LED current. The rest is maybe 50 mA combined. Some of this is sensitive analog circuitry. One device we are measuring has a nominal signal of 10 mV. The sensors are all slow, so power supply noise can and will be filtered in analog before the ADC and in digital in the delta-sigma ADC.

The switching charger circuit and the motor controller will be on a separate board at the back of the chassis, perhaps two feet/500 mm from the front of the chassis where the front panel, battery and controller board are. The motor is mostly in the back.

Some are concerned about the power wasted in the linear regulators for 5 and

3.3 volts and want them to be switchers. Rather than making them switchers, I'm thinking add a 7V switcher on the rear board to supply a voltage for linear regulators on the front controller board. Then the wasted heat that the controller board has to dissipate is much lower.

I'd really like to see a display used that doesn't consume so much current, but that ain't go'na happen. The rest of the electronics is pretty low power even when using power from the 12V rail.

There is some irony in the fact that one engineer is opposed to driving the linears directly from 12V because the higher temps will lower the reliability of the linear parts while some mechanical parts of the machine are designed for a lifetime of weeks. I'm pretty sure running a linear at

80 °C instead of 50°C is not going to make it crap out in a few weeks.

Does adding a 7V switcher to the PSU board in the rear of the chassis sound like a reasonable approach to reducing the power dissipated in the linear regulators on the front board?

What would you do?

--

Rick C.

- Get 1,000 miles of free Supercharging - Tesla referral code -

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Reply to
Tim Williams

It depends how much your power budget is when compared to the motor.

If the motor is really running at around 100W then 3W wasted in the electronics is not all that important. If the motor runs at 10W then you could get 30% more runtime with mains offline before the battery dies.

Maybe power the display with a 5W dropper resistor so that the linear regulators only have to deal with the clean analogue supply What would you do?

The supply voltages you wanted are all common on consumer PC PSUs.

--
Regards, 
Martin Brown
Reply to
Martin Brown

I like to use the little 3-lead potted things that are switcher drop-ins for 78xx regulators. That's sure easy. Most of them can be used to convert pos to neg supplies, too.

SRH05 accepts up to 72 volts in.

Reply to
John Larkin

Reply to
Rickster C

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