The custom PCB to control up to 4 individual Peliter coolers interfacing the high power laser modules.
Technical specifications:
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Input: 24VDC, max 20A.
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Output per channel: up to 10A, PWM at 5% to 100% duty cycle. 30N06L
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Recommended Peltier module: series-parallel modules supporting up to 24VDC input, with up to 50W heat transfer on the cold side.
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Temperature sensor: Dallas digital temperature sensor with Onewire interface. DS18B20
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Microcontroller (MCU) power supply: 5VDC, max 200mA. Completely separated from the 12DVC supply.
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MCU programming interface: UART over TTL, via a 6-pin connecter with the FTDI friend USB adapter.
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External set point control: I2C bus to reduce the cabling effort.
The board is primarily used to dissipate the waste heat from the 3,000mW laser modules. A high laser power is required to compensate the coupling loss of the homogenizing liquid light-guide and the TV lens, so that I can excite the fluorescence-stained mammalian cells on all 96 wells of the multi-well plate (area: 180mm x 90mm).
At the time, there was an urgent need to create an evaluation board at less than 10% of the cost of the OEM laser parts. So, the OEM provided temperature controller evaluation kits were a no go.
If I were to route the PCB again, I would have increased the pin-to-pin separation of the TO-220 package to avoid short circuit. One way to solve this is to draw a "tripod" footprint.
- The effect of pulse width modulation (PWM) frequency on the realiability of thermoelectric modules. https://tetech.com/wp-content/uploads/2013/10/ICT99MJN.pdf
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