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The linear voltage regulator is simply a
The power necessarily dissipated by the regulator can be calculated if both the external input voltage and the current drawn by the Jackrabbit board and daughterboards connected to the Jackrabbit board are known. The current provided by the
The linear regulator maintains its output voltage to within ±5% as long as the heat sink is dissipating less than 2 W. The regulator will operate outside its specifications when the heat sink is dissipating 2 W to 3.3 W. Thermal shutdown turns the regulator off above 3.3 W. Figure
| 350 |
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| 300 |
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| 3.3 W |
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| (DCIN – 5 V) |
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(mA) | 250 |
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| 2 W |
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Current | 200 |
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| Thermal |
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| shutdown |
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150 |
| Regulated |
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| Undervoltage |
| Regulated |
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| outside |
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| specifications | specifications |
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| 100 |
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| 50 | 5 | 10 | 15 | 20 | 25 | 30 | 35 |
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| DCIN (V) |
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Figure C-2. 7805 Linear Regulator Power Operating Curve
The Jackrabbit operating at 14.74 MHz with no loading at the outputs typically consumes 105 mA when the programming cable is connected, and 95 mA when the programming cable is not connected. This means that DCIN can safely be from 7.5 V to 25 V. An addi- tional 50 mA is available for a daughterboard, but the voltage regulation would suffer slightly.
80 | Jackrabbit (BL1800) |