Nick Kirkby

The DC-DC converter and A/C (air-con) motor driver…

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sits underneath the power electronics that drive the two motor/generators in a gen 2 (2004-2009) Toyota Prius.  It uses the 200V battery to drive the air conditioning system compressor and also to generate a 12V rail to charge the car battery and run stuff like lights and speakers (and all the computers n stuff).

What it looks like inside:

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The DC-DC converter is a “forward converter.”  It uses an h-bridge of IGBTs to chop 200VDC into the primary of a step-down transformer.  The output of the secondary is rectified and filtered to make a nice clean 12-14VDC.

The relevant circuit diagram (shown below) was found in the most informative and excellent Hybrid Vehicle Control Manual.

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How Turn On???

tl;dr these two connectors

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want this

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and these ring terminals want 200VDC.  Observe polarity!

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Setup Details

Here is my prius battery simulator.  It is a variac into a bridge rectifier into a couple of capacitors.

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here is my 12V “car battery.”  It is grounded to the inverter housing

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Here is +12V connected to the necessary pins and “before” shot of voltage on the 12V battery.

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After switching on the variac, the 12V battery voltage jumps up.

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and the DC clamp meter says we’re charging at half an amp.

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We’re pulling about 90mA from the 200V rail.

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The converter works down to about 140VDC.  The 12V output sags from 14V down to about 12.5V when dropping the input from 200V to 140V.  I didn’t test overvoltage on the input.  We’ll leave that the impending vehicle integration…