поискавой системы для электроныых деталей |
|
IRF7401 датащи(PDF) 9 Page - Analog Devices |
|
IRF7401 датащи(HTML) 9 Page - Analog Devices |
9 / 24 page REV. C ADN8830 –9– Although the thermistor has a nonlinear relationship to tem- perature, near optimal linearity over a specified temperature range can be achieved with the proper value of RX. First, the resistance of the thermistor must be known, where RR T T RT T RT T THERM T LOW TMID T HIGH == == == 1 2 3 @ @ @ (2) TLOW and THIGH are the endpoints of the temperature range and TMID is the average. These resistances can be found in most thermistor data sheets. In some cases, only the coefficients corresponding to the Steinhart-Hart equation are given. The Steinhart-Hart equation is 1 11 3 T ab n R c n R =+ ()+ () [] (3) where T is the absolute temperature of the thermistor in Kelvin (K = °C + 273.15), and R is the resistance of the thermistor at that temperature. Based on the coefficients a, b, and c, RTHERM can be calculated for a given T, albeit somewhat tediously, by solving the cubic roots of this equation RTHERM =+ + ++ exp –– – χχ ψ χχ ψ 24 27 24 27 2 3 1 2 1 3 2 3 1 2 1 3 (4) where X a T c = – 1 and ψ= b c RX is then found as R RR R R RR RR R X TT T T TT TT T = + + 12 2 3 13 13 2 2 2 – – (5) For the best accuracy as well as the widest selection range for resistances, RX should be 0.1% tolerance. Naturally, the smaller the temperature range required for control, the more linear the voltage divider will be with respect to temperature. The voltage at THERMIN is V VREF R RR X THERM THERM X = + (6) where VREF has a typical value of 2.47 V. The ADN8830 control loop will adjust the temperature of the TEC until VX equals the voltage at TEMPSET (Pin 4), which we define as VSET. Target temperature can be set by Vm T T V SET MID XMID = ()+ – (7) where T equals the target temperature, and m VV TT X HIGH X LOW HIGH LOW = ,, – – (8) VX for high, mid, and low are found by using Equation 6 and substituting RT3, RT2, and RT1, respectively, for RTHERM. The variable m is the change in VX with respect to temperature and is expressed in V/ °C. The setpoint voltage can be driven from a DAC or another voltage source, as shown in Figure 4. The reference voltage for the DAC should be connected to VREF (Pin 7) on the ADN8830 to ensure best accuracy from device to device. For a fixed target temperature, a voltage divider network can be used as shown in Figure 5. R1 is set equal to RX, and R2 is equal to the value of RTHERM at the target temperature. 3.3V ADN8830 8 4 7 30 AD7390 6 8 5 3.3V 7 1–4 C Figure 4. Using a DAC to Control the Temperature Setpoint 3.3V ADN8830 8 7 4 30 R2 R1 Figure 5. Using a Voltage Divider to Set a Fixed Temperature Setpoint Design Example 1 A laser module requires a constant temperature of 25 °C. From the manufacturer’s data sheet, we find the thermistor in the laser module has a value of 10 k Ω at 25°C. Because the laser is not required to operate at a range of temperatures, the value of RX can be set to 10 k Ω. TEMPSET can be set by a simple resistor divider as shown in Figure 5, with R1 and R2 both equal to 10 k Ω. Design Example 2 A laser module requires a continuous temperature control from 5 °C to 45°C. The manufacturer’s data sheet shows the thermistor has a value of 10 k Ω at 25°C, 25.4 kΩ at 5°C, and 4.37 kΩ at 45 °C. Using Equation 5, R X is calculated to be 7.68 k Ω to yield the most linear temperature-to-voltage conversion. A DAC will be used to set the TEMPSET voltage. DAC Resolution for TEMPSET The temperature setpoint voltage to THERMIN can be set from a DAC. The DAC must have a sufficient number of bits to achieve adequate temperature resolution from the system. The voltage range for THERMIN is found by multiplying the variable m from Equation 8 by the temperature range. THERMIN Voltage Range m T T MAX MIN =× () – (9) From Design Example 2, 40 °C of the control temperature range is achieved with a voltage range of only 1 V. |
Аналогичный номер детали - IRF7401 |
|
Аналогичное описание - IRF7401 |
|
|
ссылки URL |
Конфиденциальность |
ALLDATASHEETRU.COM |
Вашему бизинису помогли Аллдатащит? [ DONATE ] |
Что такое Аллдатащит | реклама | контакт | Конфиденциальность | обмен ссыками | поиск по производителю All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |